UK Consumer group Which? conducted the test that showed keyboards may actually be dirtier than a toilet seat:

Out of 33 keyboards swabbed, four were regarded as a potential health hazard and one harboured five times more germs than one of the office's toilet seats.

Microbiologist Dr Peter Wilson said a keyboard was often "a reflection of what is in your nose and in your gut".

During the Which? tests in January this year, a microbiologist deemed one of the office's keyboards to be so dirty he ordered it to be removed, quarantined and cleaned. It had 150 times the recommended limit for bacteria - five times as filthy as a lavatory seat tested at the same time, the research found.

I was occasionally asked to clean keyboards here at work, and most of the typical ones did not come apart. However, the MS Natural Keyboard was always a joy to clean... Just a few screws out, then a couple of rubber mats to wash off and keytops to soak in sudsy water. Give it all a dry and snap them back into place, and you've got a new keyboard for the most part.

My current keyboard, an old clicky IBM Model M model, can remove the keytops, but is pretty tricky to actually open up and get all the crumbs out of.

I occasionally pop a few keys off and take a damp q-tip to the area underneath. Can't take off too many, or I'll never get them back in the right place! The keyboard is still pretty nasty, but it would be worse if I never made the attempt.

There are folks who put their keyboards in the dishwasher, but I'm afraid to do that. The only time water was spilled on mine (roof leak), the laminated layers inside took so long to dry that they corroded a bit. It never worked perfectly afterward. That's a Mac keyboard; your mileage may vary.